Top 12 interview question based on DNS.
Q1: What is DNS?
Ans: DNS stands for Domain Name Server or Domain Name Service.
DNS is use to resolve FQDN to IP and IP to FQDN
Q2: What is the port
no of DNS?
Ans: Port No: 53
Q3: Explain about DNS
zones (Primary, Secondary & Stub)?
Ans: Primary Zone:
Primary
zone is store a master copy of zone data in a local file or in AD DS. In DNS
Server Primary zone is the read/write copy of the DNS database. Since the
primary zone of the DNS server is the read/write copy of the DNS database, it
must be kept at a location where it remains physically protected from attacks,
and remains safe from internal or external network threats and intrusions. By
default the primary zone file is named as zone_name.dns in %windir%System32DNS.
Secondary Zone:
Secondary
Zones are a DNS feature that allows the entire DNS database
from a Master DNS server to be transferred to the Secondary.
A Secondary Zones allows an organization to provide fault tolerance
and load balancing to internal names.
Stub Zone:
A stub zone is
a copy of a zone that contains only those resource records necessary
to identify the authoritative Domain Name System (DNS) servers for
that zone. Astub zone is used to resolve names between
separate DNS namespaces.
Q4: What is forward
and reverse lookup in DNS?
Ans: Forward DNS
Lookup:
A forward DNS lookup is when you resolve the IP address of a given
domain. For this, DNS “A” resource record is used for IPv4 address and “AAAA”
resource record for IPv6 address.
Reverse DNS Lookup:
A
reverse DNS lookup is when you want to resolve an domain name for a known IP
address. For this, DNS “PTR” resource record is used. Not all IP address have a
PTR record configured and thus reverse lookup does not give any domain. The network
administrator needs to configure PTR record for the IP addresses the
organization owns for this to work
Q5: How many records
in DNS Server?
Ans: There are 10 types of
DNS records as shows below:
1. A Record: It is also known as a DNS host record, stores a hostname and its
corresponding IPv4 address.
2. AAAA Record: It
stores a hostname and its corresponding IPv6 address.
3. CNAME Record (Canonical
Name record): It can be used to alias a hostname to another hostname.
When a DNS client requests a record that contains a CNAME, which points to
another hostname, the DNS resolution process is repeated with the new hostname.
4. MX Record (Mail exchanger
record): This specifies an SMTP email server for the domain, used to
route outgoing emails to an email server.
5. NS Record (Name Server
records): This record specifies that a DNS Zone, such as “example.com”
is delegated to a specific Authoritative Name Server, and provides the address
of the name server.
6. PTR Record
(Reverse-lookup Pointer records): It allows a DNS resolver to provide
an IP address and receive a hostname (reverse DNS lookup).
7. CERT Record (Certificate
record): It stores encryption certificates—PKIX, SPKI, PGP, and so on.
8. SRV Record (Service
Location): It is a service location record, like MX but for other
communication protocols.
9. TXT Record: It’s
typically carries machine-readable data such as opportunistic encryption,
sender policy framework, DKIM, DMARC, etc.
10. SOA Record (Start of Authority): This
record appears at the beginning of a DNS zone file, and indicates the
Authoritative Name Server for the current DNS zone, contact details for the
domain administrator, domain serial number, and information on how frequently
DNS information for this zone should be refreshed.
Q7: What is Round
Robin DNS?
Ans: Round Robin DNS is technique which used to load
distribution, load balancing or fault-tolerance internet protocol service host
like FTP Server, Webserver and manage the DNS response to address request from
client computers.
Q8: What is Dynamic
DNS?
Ans: Dynamic DNS helps for automatically updating the name servers
whenever there is a change in the IP address in the Domain Name System.
Normally when a user connects to the Internet, the user’s ISP assigns an unused
IP address from a pool of IP addresses, and this address is used only for the
duration of that specific connection. This method of dynamically assigning
addresses extends the usable pool of available IP addresses. A dynamic DNS
service provider uses a special program that runs on the user’s computer,
contacting the DNS service each time the IP address provided by the ISP changes
and subsequently updating the DNS database to reflect the change in IP address.
Q9: Before installing your
first domain controller in the network, you installed a DNS server and created
a zone, naming it as you would name your AD domain. However, after the
installation of the domain controller, you are unable to locate infrastructure
SRV records anywhere in the zone. What is the most likely cause of this failure?
Ans: The zone you created was not configured to allow dynamic
updates. The local interface on the DNS server was not configured to allow
dynamic updates.
Q10: How to verify whether DNS is working
correctly?
Ans: To verify whether DNS is working correctly start run
-> type “cmd” -> type “nslookup”.
You will get default
DNS server name and it’s IP address.
Q11: How many types of
queries in DNS?
Ans: There are two types of DNS queries:
In iterative query the
DNS server will attempt to find the website in its local cache. If it cannot
find an answer it will not ask other DNS servers but will reply back to the
original request with a single “I don't know, but you could try asking
this server” message.
2. Recursive Query:
In recursive query DNS
server will attempt to find the website in its local cache. If it cannot find
an answer it will query other DNS servers on your behalf until it finds the
address. It will then respond to the original request with the results from
each server's query
Q12: What is caching
only server in terms of DNS?
Ans: Caching-only servers are those DNS servers that only perform name
resolution queries, cache the answers, and return the results to the client.
Once the query is stored in cache, next time the query in resolved locally from
cached instead of going to the actual site.
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